Principal objectives for the studies proposed for the coming budget year include: (1)\further characterization of the cellular components involved in induction and maintenance of lymphocyte colonies (LC); (2)\characterization of the role of well-defined lymphokines and other growth and differentiation factors in determining the phenotypic and functional characteristics of cells within colonies; and (3)\development of a better understanding of factors controlling the "social behavior" of lymphocytes grown in semisolid media. Characterization of cells involved in LC induction and maintenance will be performed chiefly by depletion/replacement type experiments that rely on several cell fractionation techniques (panning, fluorescence-activated cell sorting, elutriation). Recent experiments using counterflow centrifugation elutriation to fractionate human bone marrow have provided an excellent source of lymphocyte-depleted marrow cells for the study of lymphopoiesis. Colonies arising from mature lymphoid cells and their precursors will be contrasted with respect to mechanisms of colony formation. The availability of relatively homogeneous preparations of interleukins 1 and 2 (IL-2) and the availability of several different non-IL-2-containing lymphocyte-growth factors through collaborative arrangements will facilitate a detailed analysis of the effect of these lymphokines on LC growth. Finally, the net effects of cell subset enrichment and depletion and the addition of exogenous lymphokines will be monitored by time lapse cinemicroscopic techniques. Efforts will be made to develop more objective and quantitative means for analysis of cinemicrographic data. (LB)